Abstract
To the Editor,
In a recent letter, Dr Brian Payne, the pioneer of calcium adjustment, endorsed the concept of normalisation of adjusted equation to a mean of 2.4 mmol/L.
By normalising mean calcium to 2.4 mmol/L in the adjustment equation, we make an assumption that this value agrees with the population mean universally. According to NEQAS data, 5% of United Kingdom (UK) biochemistry laboratories measure calcium using Siemens Advia analysers. Previous reports highlighted a calibration issue with the Siemens calcium assays 1 and this calibration error resulted in a lower reference range of 2.12–2.51 mmol/L (mid-point 2.31 mmol/L). 2 Imposing a value of 2.4 on Siemens users will shift adjusted calcium results away from the normal range and potentially mask hypocalcaemia.
Variation in calcium reference ranges.
The literature shows that using population mean value for calcium outperforms the traditional Payne’s equation. 4 In the era of data mining and advanced laboratory information systems, clean data, reflecting the population of choice and the analytical platform in use, can be easily obtained. This approach has been validated against ionised calcium and represents an evidence-based approach. While I share the pragmatist’s aspiration for harmonisation, I take the view that the road for harmonisation of adjusted calcium begins with harmonisation of albumin methods, rather than the use of a fixed factor for calcium mean.
Footnotes
Acknowledgements
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Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Ethical approval
Not applicable.
Guarantor
NJ.
Contributorship
Nuthar Jassam sole author.
